Gas generator for airbag

ABSTRACT

A gas generator for air bags for use in an air bag system for safely protecting a driver and riders in a vehicle from shock from collisions. The gas generator has the following features to enable a component count to be reduced, thereby manufacturing the gas generator at low cost, while preventing slag in a gas flowing outside.  
     The gas generator includes a housing ( 3 ) formed by a side cylinder ( 1   b ) with a plurality of gas exhaust openings ( 8 ) being closed at its ends by an upper cap ( 1   a ) and a lower cap ( 2   a ); an igniting device ( 16 ), provided in the housing ( 3 ) at a center portion thereof, for generate flame; gas generating agents ( 6 ), provided in the housing ( 3 ) at a location radially outside of the igniting device ( 16 ), to be burnt by the flame to generate gas; a cooling/filtering member ( 7 ) provided in the housing ( 3 ) at a location radially outside of the gas generating agents ( 6 ) to enclose the gas generating agents and extending from the side of the upper cap ( 1   a ) to the side of the lower cap ( 2   a ); and an annular projection ( 50 ) for preventing the gas generated by the burning of the gas generating agents ( 6 ) from flowing toward an end portion of the cooling/filtering member ( 7 ). The annular projection ( 50 ) is integrally formed on at least one of the upper cap ( 1   a ) and the lower cap ( 2   a ) so as to abut with an inner peripheral surface of the cooling/filtering member ( 7 ).

TECHNICAL FIELD

[0001] The present invention relates to a gas generator for air bags(hereinafter it is simply referred to as “gas generator”) for use in anair bag system for safely protecting a driver and riders in a vehiclefrom shock from collisions. Particularly, the present invention relatesto a gas generator of cost efficiency having capabilities of maintainingthe performance capability of preventing slag in a gas flowing outside,despite of reduction of a component count.

BACKGROUND ART

[0002] The gas generators of this type include the one having a housingconstruction of the so-called single cylinder type and the one having ahousing construction of the so-called double cylinder type. Thesehousing constructions include a welded one and a friction welded one.Either of these two types of gas generators have the followingfundamental construction. That is to say, these gas generators have ahousing formed by a side cylinder having a plurality of gas exhaustopenings; an upper cap closing an upper end of the side cylinder; and alower cap closing a lower end of the side cylinder. The housing containstherein an igniter, gas generating agents, and a cooling/filteringmember, which are arranged in this order from the center of the housingto a radially outside of the same. The cooling/filtering member isformed to enclose the gas generating agents, extending from the uppercap side to the lower cap side.

[0003] In the gas generator having this fundamental construction,pressure of the gas generated in the housing rises instantaneously toinflate the housing at the time of activation of the gas generator,according to the types of gas generating agents or burning conditions.As a result of this, looseness may occur in both end portions of thecooling/filtering member in abutment with the upper cap and the lowercap, then causing degradation of the hermeticity of thecooling/filtering member at the ends abutting with the upper and lowercaps, and as such may cause the slag in the gas to flow outside. Theinventors of this application previously applied for patent in respectof a gas generator having the construction of presenting the slag in gasfrom flowing outside even when the gas pressure rises instantaneously(Japanese patent application No. Hei 8(1996)-207929).

[0004] Specifically, the previously proposed gas generator has, as shownin FIG. 3, a housing 33 composed of a side cylinder 31 b having aplurality of gas exhaust openings 38; an upper cap 31 a closing an upperend of the side cylinder 31 b; and a lower cap 32 a closing a lower endof the side cylinder 31 b. The housing 33 includes therein an igniter70, gas generating agents 36, and a cooling/filtering member 37, whichare arranged in this order from the center of the housing to a radiallyoutside thereof. The cooling/filtering member 37 is formed to extendfrom the side of the upper cap 31 a to the side of the lower cap 32 a.

[0005] Further, the housing 33 has therein metallic foil 39, bypasspreventing members 45, 46 and sealing members 40 a, 40 b. The metallicfoil 39 is adheres on an inner wall of the side cylinder 31 b to cap thegas exhaust openings 38 from the inside. The bypass preventing members45, 46 are provided at the opposite ends of the cooling/filtering member37. The bypass preventing members 45, 46 have a L-shaped section,contacting with an inner surface of the cooling/filtering member 37 atthe opposite end portions thereof and with inner surfaces of the upperand lower caps 31 a, 32 a. To well ensure the effect of preventing theslag from flowing outside, the sealing members 40 a, 40 b are providedat end surfaces of the cooling/filtering member 37.

[0006] With the gas generator thus constructed, even when the gaspressure in the housing rises instantaneously to inflate the housing,since the bypass preventing members 45, 46 are located at the oppositeends of the cooling/filtering member 37, the slag in the gas can beprevented flowing outside. However, disadvantageously, the gas generatorthus constructed provides increased component count and thus increasedcosts, due to the provision of the bypass preventing members 45, 46.Particularly in the circumstance in which specs on air bag systems arebeing standardized, cost reduction is being increasingly requested forgas generators, so cost increase resulting from the increase incomponent count is a significant drawback.

[0007] Accordingly, it is the object of the present invention to providean improved gas generator at a low cost by improving the construction ofinner surfaces of the upper and lower caps 31 a, 32 a to produce thefunction that is equal to or better than the function of the bypasspreventing members 45, 46 of preventing the slag in the gas from flowingoutside through the cooling/filtering member 37, thereby eliminating theneed of the bypass preventing members 45, 46 to provide reduction ofcomponent count and a resultant improved efficiency in assembling work.

DISCLOSURE OF THE INVENTION

[0008] A gas generator for air bags of the present invention comprises ahousing formed by a side cylinder with a plurality of gas exhaustopenings being closed at its ends by an upper cap and a lower cap; anigniting means, provided in the housing at a center portion thereof, forgenerate flame; gas generating agents, provided in the housing at alocation radially outside of the igniting means, to be burnt by theflame to generate gas; a cooling/filtering means provided in the housingat a location radially outside of the gas generating agents to enclosethe gas generating agents and extending from the side of the upper capto the side of the lower cap; and an annular projection means forpreventing the gas generated by the burning of the gas generating agentsfrom flowing toward an end portion of the cooling/filtering means, theannular projection means being integrally formed on at least one of theupper cap and the lower cap so as to abut with an inner peripheralsurface of the cooling/filtering means.

[0009] This produces the gas generator having, as compared with the gasgenerator as illustrated in FIG. 3, the feature that the bypasspreventing members are substituted by the annular projection meansintegrally formed with the upper cap or the lower cap, thus providingreduced component count than the gas generator of FIG. 3.

[0010] The annular projection means has the same function of preventingthe gas flowing toward the end portion of the cooling/filtering memberas the bypass preventing members, and as such can allow a full amount ofgas to pass through the entire cooling/filtering member except the endportion thereof. Further, when an instantaneous pressure rise occurs atthe time of burning, the annular projection means is pressed toward thecooling/filtering member, and as such can produce the operation andeffect of a further increased degree of contact between the end surfaceof the annular projection means at the outer diameter side thereof andthe end surface of the cooling/filtering member at the inner diameterside thereof. This enables the slag in the gas to be prevented flowingoutside more reliably. This can achieve the gas generator havingimproved cost efficiency resulting from the reduced component count andthe resultant improved assembling workability, while fully maintainingits performance capability of reliably preventing the slag in the gasflowing outside within a permissible range, without using any bypasspreventing members shown in FIG. 3 and irrespective of the types of gasgenerating agents and the burning conditions.

[0011] The gas generator for air bags of the present invention may takethe embodied form that the side cylinder and the upper cap areintegrally formed and the side cylinder and the lower cap are joined toeach other by friction welding, to thereby form the housing.

[0012] This embodied form provides the following result. When thehousing is formed by friction welding, it is difficult to bring the sidecylinder and the lower into full contact with each other in a uniformcondition, and as such may often produce the housing with a gapdeveloping at the opposite ends of the cooling/filtering means. However,even in the gas generator having such a housing, since the projectionmeans prevents the gas flowing toward the end portion, the slag can bewell prevented flowing outside.

[0013] Also, the gas generator for air bags of the present invention maytake the embodied form that the side cylinder of thin-plate and theupper cap are integrally formed and the side cylinder and the lower capare joined to each other by welding, to thereby form the housing.

[0014] This embodied form provides the following result. The housinghaving the thin-plate welded structure is easily deformed by thepressure resulting from the gas generated, and as such may often producethe housing with a gap developing between the end of thecooling/filtering member and the cap. However, even in the housing thusstructured, since the projection means prevents the gas flowing towardthe end portion, the slag can be well prevented flowing outside.

[0015] In the gas generator for air bags of the present invention, it ispreferable that a space is formed between the cooling/filtering meansand the side cylinder.

[0016] This provides the following results. The gas is reserved in thespace formed between the cooling/filtering means and the side cylinderprior to being exhausted to the outside passing through the gas exhaustopenings, whereby the gas is rendered uniform in pressure in the space.As a result of this, occurrence of the phenomenon of the gas locallypassing through the cooling/filtering means toward the gas exhaustopenings is prevented, and as such can allow the gas to pass through theentire cooling/filtering member generally uniformly. Thus, although thegas is prevented directly flowing into the cooling/filtering means atthe end thereof by the annular projection means, after flowing from acenter portion of the cooling/filtering means into the interior thereof,the gas is allowed to easily pass through the cooling/filtering means atthe end portion thereof as well which is located at the back side of theend surface of the projection means at the outer diameter side thereof.This provides an improved efficiency of use of the cooling/filteringmeans, and as such can achieve size reduction of the cooling/filteringmeans. As a result of this, size reduction and weight reduction of thegas generator can be realized.

[0017] Further, the gas generator for air bags of the present inventionmay take the embodied form that the housing is provided, around theigniting means, with a center cylinder for joining the upper cap and thelower cap.

[0018] With the construction in which the center cylinder for joiningthe upper cap and the lower cap is provided around the igniting means,the housing is increased in rigidity and thus is made resistant todeformation even when the gas pressure rises at the burning of the gasgenerating agents. Accordingly, the annular projection means can be maderelatively small, and resultantly the material costs required for theupper cap and the lower cap can be saved and also the process time canbe shortened, thus providing reduced manufacturing costs.

[0019] For the gas generator for air bags of the present invention, itis preferable that the cooling/filtering means has a wall thicknessportion to abut with an inner wall surface of the side cylinder.

[0020] This provides the result that the pressure of the gas generatedpresses the cooling/filtering means toward the side cylinder and, as aresult, the wall thickness portion is pressed against the side cylinderand is brought into firm contact with it. This enables the slag to bereliably prevented flowing outside through the gas exhaust openings.

[0021] Further, in the gas generator for air bags of the presentinvention, the gas exhaust openings are hermetically sealed withaluminum foil.

[0022] This can provide the result that the combustion pressure can becontrolled by, for example, adjusting the thickness of the aluminum foiland also degradation of the gas generating agents resulting from theirmoisture proof can be prevented.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023]FIG. 1 is a schematic sectional view of one embodiment of thepresent invention;

[0024]FIG. 2 is a schematic sectional view of a principal part ofanother embodiment of the present invention; and

[0025]FIG. 3 is a schematic sectional view of a principal part of aconventional type of gas generator.

BEST MODE FOR CARRYING OUT THE INVENTION

[0026] The embodiments of the present invention will be described belowwith reference to the drawings.

[0027]FIG. 1 is a conceptual sectional view of one embodiment of thepresent invention. As shown in FIG. 1, the gas generator has a housing 3made of aluminum. The housing 3 is composed of an upper container 1 anda lower container 2. The upper container 1 has an upper cap 1 a; a sidecylinder 1 b extending downwardly from a periphery of the upper cap 1 a;and a center cylinder 1 c extending downwardly from a lower surface ofthe upper cap 1 a at the inside thereof. The side cylinder 1 b and thecenter cylinder 1 c are thin-plate form and are joined to the lowercontainer 2 at the lower ends thereof by friction welding.

[0028] The lower container 2 is composed of a lower container 2 a, aflanged cylinder 2 b and a side flange 2 c. A first step portion 2 e towhich the center cylinder 1 c is joined is formed on an upper surface ofthe lower cap 2 a at an inside thereof, and a second step portion 2 d towhich the side cylinder 1 b is joined is formed on the upper surface ofthe lower cap at an outside thereof. The flanged cylinder 2 b extendsupwardly from a periphery of the lower cap 2 a to enclose the sidecylinder 1 b of the upper container 1, and the side flange 2 c extendshorizontally from an upper end of the flanged cylinder 2 b.

[0029] The gas generator having the housing 3 thus constructed is whatis called the double cylinder type of gas generator having the frictionwelded housing construction, having an igniting chamber A enclosed bythe center cylinder 1 c and a gas generating chamber B enclosed by thecenter cylinder 1 c and the side cylinder 1 b. The center cylinder 1 chas a side surface forming therein a plurality of circumferentiallyarranged flame exhausting holes 18 through which the igniting chamber Ais communicated with the gas generating chamber B. The side cylinder 1 bhas a side surface forming therein a plurality of circumferentiallyarranged gas exhaust openings 8 through which the gas generating chamberB is communicated to the outside. In the igniting chamber A, an ignitingdevice 16 composed of an inflammation agent 15 and an igniter 14 isdisposed to generate flames. In the gas generating chamber B are housedgas generating agents 6 from which gas is evolved by the flames. Thisproduces the result that when the inflammation agent 15 is ignited inthe igniting chamber A, the flames pass through the flame exhaustingholes 18 to burn the gas generating agents 6, so as to evolve the gastherefrom. Then, the gas is exhausted to the outside through the gasexhaust openings 8.

[0030] The gas generating agents 6 are packed in the housing rangingfrom the side of the upper cap 1 a of the upper container 1 to the sideof the lower cap 2 a of the lower container 2. A cap 5, which can becalled as a covering member for the gas generating agents, is interposedbetween the gas generating agents 6 and the lower cap 2 a. The cap 5 hasa bottom portion 5 c located near and extending along the upper surfaceof the lower cap 2 a; a short outer cylinder portion 5 a extendingupwardly from an outer periphery of the bottom portion 5 c; and a shortinner cylinder portion 5 b extending upwardly from an inner periphery ofthe bottom portion 5 c. The short inner cylinder portion 5 b has a tip 5d formed by being bent toward the center cylinder 1 c. The tip 5 b isfixed by means of a press-contacting burr 11 produced in the outersurface of the center cylinder 1 c at the time of friction welding. Thecap 5 is provided with a cushion material 4 having resiliency. Thecushion material 4 fixedly holds the gas generating agents 6, contactingwith the gas generating agents 6.

[0031] The gas generating agents 6 are enclosed with thecooling/filtering member 7 which can allow only the gas to pass throughit. The cooling/filtering member 7 is provided extending from the sideof the upper cap 1 a to the side of the lower cap 2 a and is formed intoa cylindrical form opening at the opposite ends. The cooling/filteringmember 7 has at a lower part thereof a wall thickness portion 7 a havinga larger outer diameter than the remaining parts. The wall thicknessportion 7 a has a nose end surface, an upper slant surface and a lowerslant surface, and the nose end surface is press-fitted into an innerperipheral surface of the side cylinder 1 b. The lower slant surfaceabuts with a press-contacting burr 12 produced in the inner surface ofthe side cylinder 1 b at the time of friction welding. This provides theresult that the wall thickness portion 7 a is compressed by the sidecylinder 1 b, while abutting with the press-contacting burr 12, andthereby the cooling/filtering member 7 is brought into intimate contactwith the side cylinder 1 b to be fixed thereto. This can produce theresult that when the gas is generated, the slag in the gas can surely beprevented flowing outside from the outer peripheral surface of thecooling/filtering member 7 at a lower part thereof in the housing 3.

[0032] An inner peripheral surface of the cooling/filtering member 7 atan upper end portion thereof abuts with an annular projection 50, and aninner peripheral surface of the cooling/filtering member 7 at a lowerend portion thereof abuts with the short outer cylinder portion 5 a ofthe cap 5. The annular projection 50 is integrally formed on a lowersurface of the upper cap 1 a of the upper container 1 and has a sectionof a generally right angled triangle formed by a slant surface 50 a atthe inner diameter side and a vertical surface 50 b at the outerdiameter side. The vertical surface 50 b abuts with the inner peripheralsurface of the cooling/filtering member 7 and thereby has the functionof positioning the cooling/filtering member 7 and of preventing the gasflowing near the inner peripheral surface at the upper end portion ofthe cooling/filtering member 7 from passing through the upper endportion of the same.

[0033] This provides the result that at the time of burning, an upperlayer of gas generated in the gas generating chamber B is introduced toa center portion of the cooling/filtering member 7, except the upper endportion thereof, to pass through the center portion by the slant surface50 a of the annular projection 50. As a result of this, there is almostno fear of the slag flowing outside from a gap between the upper endportion of the cooling/filtering member 7 and the upper cap 1 a. Inaddition, even when a force acting in a direction for the inner surfaceof the upper cap 1 a and the upper end portion of the cooling/filteringmember 7 to be moved away from each other is caused by the instantaneouspressure rise in the housing at the burning, since the gas is sealed outin the part of the vertical surface 50 b of the annular projection 50,the slag is prevented flowing outside from the gap between the upper endportion of the cooling/filtering member 7 and the upper cap 1 a.

[0034] The cooling/filtering member 7 defines a space S as a gas domebetween the outer surface of the cooling/filtering member 7 and theinner peripheral surface of the side cylinder 1 b. The width of thespace S is set to be circumferentially uniform, particularly at thelocation of the gas exhaust openings 8. The space S operates to renderthe gas generated by the burning of the gas generating agents uniform,to prevent a drifting phenomenon of the gas flowing locally into thecooling/filtering member 7 toward the gas exhaust openings 8 of minimumpressure, so as to allow the gas to pass through the entirecooling/filtering member 7 generally evenly. As a result of this,despite of the provision of the annular projection 50 by which the gasis introduced to the center portion of the cooling/filtering member 7,the gas tends to flow also to the upper portion of the cooling/filteringmember 7 located at the back side of the vertical surface 50 b at theouter diameter side of the projection 50. This can provide increasedefficiency of use of the cooling/filtering member 7 to fully meet thedemand of reduction in size and weight of the gas generator.

[0035] Aluminum foil 9 adheres on the inner peripheral surface of theside cylinder 1 b at a location corresponding to the gas exhaustopenings 8. The aluminum foil 9, by means of which the gas exhaustopenings 8 are hermetically sealed, enables the burst pressure or thecombustion pressure of the gas generating agents 6 to be controlled byadjusting its thickness, for example, and also prevents degradation ofthe gas generating agents 6 resulting from their moisture proof.

[0036] Additionally, sealing members (equivalent to 40 a in FIG. 3) maybe provided between the cooling/filtering member 7 and the upper cap 1 aand between the cooling/filtering member 7 and the lower cap 1 b,respectively. This can produce the result of the slag being preventedflowing outside from the gap between the upper end of thecooling/filtering member 7 and the upper cap 1 a more reliably.

[0037] In the construction above, after the upper container 1 is madereadiness for the assemble of the gas generator, the gas exhaustopenings 8 in the upper container 1 are sealed by the aluminum foil 9.Thereafter, the inflammation agent 15 is charged in the igniting chamberA, and then the cooling/filtering member 7 is press-fitted into the gasgenerating chamber B to abut against the vertical surface 50 b of theannular projection 50. Then, the gas generating agents 6 are packed inthe inner periphery portion of the cooling/filtering member 7 and thenare fixed by pressing the cap 5 onto the upper surface of the gasgenerating agents 6.

[0038] Then, after abutted with the side cylinder 1 b and the centercylinder 1 c of the upper container 1, the lower container 2 is rotated,keeping the upper container 1 in a fixed state, whereby the lowercontainer 2 and the upper container 1 are joined to each other byfriction welding. Thereafter, the igniter 14 is fixed to the lowercontainer 2 to complete the assemble of the gas generator. This assemblycan provide reduced number of assembling processes, as compared with theconventional assembly shown in FIG. 3 in which the bypass preventingmember 45 is fixed to the upper end portion of the gas generator, andthus can provide reduced costs required for the assembly.

[0039] The gas generator assembled in the above-said assembling steps isactivated by supplying an igniting current to the igniter 14. When theigniter 14 is ignited by the supply of the igniting current and theflames burn the inflammation agent 15, the flames in the ignitingchamber A pass through the flame exhaust holes 18 into the gasgenerating chamber B, to burn the gas generating agents 6 so as togenerate gas. When the gas generated in the gas chamber B passes throughthe cooling/filtering member 7 into the space S and the internalpressure reaches a preset pressure, the aluminum foil 9 is ruptured toopen the gas exhaust holes 8, so that the gas is exhausted out from thegas exhaust holes 8.

[0040] The gas existing at the side of the upper cap 1 a (the upperlayer of gas) moves along the slant surface 50 a of the annularprojection 50, so that it is introduced into the center portion of thecooling/filtering member 7 by the slant surface. Also, the gas pressesthe annular projection 50 toward the cooling/filtering member 7, so thatthe vertical surface 50 b of the annular projection 50 and thecooling/filtering member 7 are firmly abutted with each other. As aresult of this, even if a gap is formed between the upper end surface ofthe cooling/filtering member 7 and the upper cap 1 a due to a pressurerise in the gas generating chamber B, there is almost no fear of theslag flowing outside through such a gap.

[0041] Also, if a gap develops between the cooling/filtering member 7and the cap 5, the slag will move into between the lower surface of thecooling/filtering member 7 and the lower cap 2 a. At that time, the wallthickness portion 7 a is brought into firm contact with the sidecylinder 1 b and the press-contacting burr 12, because the wallthickness portion 7 a of the cooling/filtering member 7 is abutted withthe side cylinder 1 b and the press-contacting burr 12 and because thegas pressure presses the cooling/filtering member 7 toward the sidecylinder 1 b and the press-contacting burr 12. Therefore, even if such agap develops between the cooling/filtering member 7 and the cap 5, theslag cannot move into the space S and, as a result, cannot be allowed toflow outside through the gas exhaust openings 8.

[0042] Then, as a result of the gas arriving at the space S beingrendered uniform in pressure in the space S, the gas passing through thecooling/filtering member 7 flows in generally uniform density throughoutthe cooling/filtering member 7, and as such can allow the gas to easilypass through the cooling/filtering member 7 at the upper end portionthereof as well which is located at the back side of the verticalsurface 50 b at the outer diameter side of the annular projection 50.

[0043] As mentioned above, in the conventional type of gas generatorshown in FIG. 3, the bypass preventing members are required to be set inplace and thus the assembling work have to be done at much expense intime and effort and with care, for the reason of which the assemblingwork is not necessarily easy and thus has room for improvement inproductivity. According to the gas generator of the illustratedembodiment of the invention, the assembling work can be simplified tothe extent to which the bypass preventing members can be eliminated, sothat the productivity can be improved. This can achieve the gasgenerator having improved cost efficiency associated with the improvedassembling workability resulting from the reduced component count, whilemaintaining its good performance capability of preventing the slagflowing outside.

[0044] Referring now to FIG. 2, another embodiment of the presentinvention will be described. The gas generator shown in FIG. 2 is thesingle cylinder type of gas generator having a welded structure. Whencompared with the embodiment of FIG. 1, the embodiment of FIG. 2 ismainly characterized in that there is not provided the center cylinder 1c of FIG. 1 and that the same construction as the annular projection 50formed in the upper cap 1 a is adopted in the lower cap as well.

[0045] Speaking to the construction of the annular projection 60 adoptedin the lower cap as well, in FIG. 2, the annular projection 60 isintegrally formed on a upper surface of the lower cap 22 a and has asection of a generally right angled triangle formed by a slant surface60 a at the inner diameter side and a vertical surface 60 b at the outerdiameter side. The annular projection is located so that the verticalsurface 60 b at the outer diameter side thereof can abut with the innersurface of a cooling/filtering member 27 at the lower end thereof. Thisprovides the result that the gas generated in the gas generating chamberB flows along the slant surface 50 a of the upper annular projection 50and the slant surface 60 a of the lower annular projection 60 asindicated by arrows and is all introduced to a center portion of thecooling/filtering member 27, except the upper and lower end portionsthereof, to pass through the center portion. As a result of this,despite of the construction eliminating therefrom the bypass preventingmembers used hitherto, there is almost no fear of the slag flowingoutside from gaps developing at the upper and lower end portions of thecooling/filtering member 27.

[0046] In the gas generator of this embodiment as well, sealing members(which are equivalent to 40 a, 40 b of FIG. 3) may additionally beprovided between the upper end portion of the cooling/filtering member27 and the upper cap 21 a and between the lower end portion of thecooling/filtering member and the lower cap 22 a, respectively.

[0047] According to the gas generator of this embodiment, the bypasspreventing members in the gas generator of FIG. 3 are not at allrequired, so the assembling work of the gas generator can be done withimproved efficiency. As a result of this, the gas generator can berealized at a lower cost by virtue of further reduced component countand improved assembling work efficiency.

[0048] The section form of the annular projection 50, 60 is not limitedto the illustrated ones in FIGS. 1 and 2. Modifications, including, forexample, varying the size, forming the vertical surface 50 b or 60 binto a curved surface, varying the angle of the vertical surface,forming the slant surface 50 a or 60 a at the inner diameter side into acurved surface and forming it into a stepped surface, belong in a matterof design choice, in consideration of gas generating agents used andburning conditions.

[0049] In the discussion above, the friction-welded housing structurehaving two outer and inner side cylinders is illustrated in FIG. 1 asthe housing construction to which the concept of the bypass preventingmechanism embodied by the annular projection is applicable, though suchconcept may of course be effectively applied to the welded housingstructure and the friction-welded housing structure of a singlecylinder. In addition, the welded housing structure having the singleside cylinder is illustrated in FIG. 2, though the concept of theinvention is of course applicable to the housing structure of doublecylinder type. The materials which may be used for the welded housingstructure include metallic materials, such as stainless steel, inaddition to aluminum.

[0050] As seen from the foregoing, the gas generator of the embodimentas illustrated in for example FIG. 1 includes the housing 3 formed bythe side cylinder 1 b having a plurality of gas exhaust openings 8 beingclosed at the ends thereof by the upper cap 1 a and the lower cap 2 a;the igniting device 16, provided in the housing 3 at a center partthereof, for generate flame; the gas generating agents 6, provided inthe housing 3 at a location radially outside of the igniting device 16,to be burnt by the flame and generate gas; the cooling/filtering member7, provided in the housing 3 at a location radially outside of the gasgenerating agents 6 and extending from the side of the upper cap 1 a tothe side of the lower cap 2 a, to enclose the gas generating agents 6;and the annular projection 50 for preventing the gas generated by theburning of the gas generating agents 6 from flowing toward the ends ofthe cooling/filtering member 7, the annular projection 50 beingintegrally formed on at least one of the upper cap 1 a and the lower cap2 a so as to abut with the inner peripheral surface of thecooling/filtering member 7.

[0051] As a result of this, the inventive gas generator has, as comparedwith the gas generator as illustrated in FIG. 3, the feature that thebypass preventing members are substituted by the annular projection 50integrally formed with the upper cap 1 a or the lower cap 2 a, thusproviding reduced component count than the gas generator of FIG. 3.

[0052] The annular projection 50 has the same function of preventing thegas flowing toward the end of the cooling/filtering member 7 as thebypass preventing members, and as such can allow a full amount of gas topass through the entire cooling/filtering member 7 except the oppositeend portions thereof. Further, when an instantaneous pressure riseoccurs in the housing, the gas generated presses the annular projection50 toward the cooling/filtering member 7, and as such can produce theoperation and effect of a further increased degree of contact betweenthe end surface of the annular projection 50 at the outer diameter sidethereof and the end surface of the cooling/filtering member 7 at theinner diameter side thereof. This enables the slag in the gas to beprevented flowing outside more reliably. This can achieve the gasgenerator having improved cost efficiency resulting from the reducedcomponent count and the resultant improved assembling workability, whilefully maintaining its performance capability of reliably preventing theslag flowing outside within a permissible range, without using anybypass preventing members and irrespective of the types of gasgenerating agents 6 and the burning conditions.

[0053] When the gas generator has the construction that the space S isformed between the cooling/filtering member 7 and the side cylinder 1 b,the gas is reserved in the space S formed between the cooling/filteringmember 7 and the side cylinder 1 b prior to being exhausted to theoutside passing through the gas exhaust openings 8, whereby the gas isrendered uniform in pressure in the space S. As a result of this,occurrence of the phenomenon of the gas locally passing through thecooling/filtering member 7 toward the gas exhaust openings 8 isprevented, and as such can allow the gas to pass through the entirecooling/filtering member 7 generally uniformly. Thus, although the gasis prevented directly flowing into the cooling/filtering member 7 at theends thereof by the annular projection 50, after flowing from a centerportion of the cooling/filtering member 7 into the interior thereof, thegas is allowed to pass through the entire cooling/filtering member 7generally uniformly, as mentioned above. This improves the flow of thegas into the end portion of the cooling/filtering member 7 located atthe back side of the end surface of the annular projection 50 at theouter diameter side thereof, thus providing an improved efficiency ofuse of the cooling/filtering member 7. As a result of this, sizereduction and weight reduction of the gas generator can be realized.

[0054] With the construction in which the side cylinder 1 b isintegrally formed with the upper cap 1 a and also is joined to the lowercap 2 a by friction welding to thereby form the housing 3 of the gasgenerator, it is generally difficult to bring the side cylinder 1 b andthe lower cap 2 a into full contact with each other in a uniformcondition, and as such may often produce the housing 3 with a gapdeveloping at the opposite ends of the cooling/filtering member 7.However, despite of the gas generator having the thus formed housing 3,since the projection 50 prevents the gas flowing toward the end portion,the slag can be well prevented from flowing outside.

[0055] With the construction in which the thin-plate-like side cylinder1 b is integrally formed with the upper cap 1 a and also is joined tothe lower cap 2 a by welding to thereby form the housing 3 of the gasgenerator, the housing 3 having the thin-plate welded structure iseasily deformed by the pressure resulting from the gas generated, and assuch may often produce the housing 3 with a gap developing at the end ofthe cooling/filtering member 7. However, even in this case, since theprojection 50 prevents the gas flowing toward the end portion, the slagcan be well prevented flowing outside.

[0056] With the construction in which the center cylinder for joiningthe upper cap 1 a and the lower cap 2 a is provided around the ignitingdevice 16 of the housing 3, the housing 3 is increased in rigidity andis made resistant to deformation even when the gas pressure rises at theburning of the gas generating agents 6. Accordingly, the annularprojection 50 can be made relatively small, and resultantly the materialcosts required for the upper cap 1 a and the lower cap 2 a can be savedand also the process time can be shortened to reduce the manufacturingcosts.

[0057] In the case where the cooling/filtering means is provided withthe wall thickness portion to abut with the inner wall surface of theside cylinder, the pressure of gas generated presses thecooling/filtering member 7 toward the side cylinder 1 b. As a result,the wall thickness portion is pressed against the side cylinder 1 b andis brought into firm contact with it, so that the slag is preventedflowing outside through the gas exhaust openings 8.

[0058] With the gas generator having the construction in which the gasexhaust openings 8 are hermetically sealed with the aluminum foil 9, thecombustion pressure can be controlled by adjusting the thickness of thealuminum foil 9 and also degradation of the gas generating agents 6resulting from their moisture proof can be prevented.

CAPABILITIES OF EXPLOITATION IN INDUSTRY

[0059] The present invention enables the gas generator to bemanufactured at low cost, by providing the reduced component count andthe resultant improved assembling workability resulting from eliminationof the need for the bypass preventing members used hitherto, whilemaintaining its performance capability of preventing the slag in the gasflowing outside from the cooling/filtering member.

1. A gas generator for air bags comprising: a housing formed by a sidecylinder with a plurality of gas exhaust openings being closed at itsends by an upper cap and a lower cap; an igniting means, provided insaid housing at a center portion thereof, for generate flame; gasgenerating agents, provided in said housing at a location radiallyoutside of said igniting means, to be burnt by said flame to generategas; a cooling/filtering means provided in said housing at a locationradially outside of said gas generating agents to enclose said gasgenerating agents and extending from the side of said upper cap to theside of said lower cap; and an annular projection means for preventingthe gas generated by the burning of said gas generating agents fromflowing toward an end portion of said cooling/filtering means, saidannular projection means being integrally formed on at least one of saidupper cap and said lower cap so as to abut with an inner peripheralsurface of said cooling/filtering means.
 2. An gas generator for airbags as set forth in claim 1 , wherein said side cylinder and said uppercap are integrally formed and said side cylinder and said lower cap arejoined to each other by friction welding to form said housing.
 3. An gasgenerator for air bags as set forth in claim 1 , wherein said sidecylinder and said upper cap are integrally formed and said side cylinderof thin-plate and said lower cap are joined to each other by welding toform said housing.
 4. An gas generator for air bags as set forth in anyone of claims 1 to 3 , wherein a space is formed between saidcooling/filtering means and said side cylinder.
 5. An gas generator forair bags as set forth in any one of claims 1 to 3 , wherein said housingis provided, around said igniting means, with a center cylinder forjoining said upper cap and said lower cap.
 6. An gas generator for airbags as set forth in claim 4 , wherein said housing is provided, aroundsaid igniting means, with a center cylinder for joining said upper capand said lower cap.
 7. An gas generator for air bags as set forth inclaim 1 , wherein said cooling/filtering means has a wall thicknessportion to abut with an inner wall surface of said side cylinder.
 8. Angas generator for air bags as set forth in claim 1 , wherein said gasexhaust openings are hermetically sealed with aluminum foil.